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MathGroup Archive 2006

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Re: List difference using patterns and substitutions.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg71335] Re: List difference using patterns and substitutions.
  • From: dh <dh at metrohm.ch>
  • Date: Wed, 15 Nov 2006 06:43:40 -0500 (EST)
  • Organization: hispeed.ch
  • References: <ejc53g$6qf$1@smc.vnet.net>


Hi Nacho,

simply drop the first element from your list and subtract from it the 

list with the last element removed:

Drop[list, 1] - Drop[list, -1]

or another possibility:

Rest[list]-Most[list]

Daniel



Nacho wrote:

> Hello.

> 

> I'm trying to figure how can I build a difference list from another

> using only patterns and rule substitutions.

> 

> The idea is to get from a list, another, one element shorter, where

> each value is the substraction of two consecutive elements in the

> original list, that is, from {1,2,3,5,5} get {1,1,2,0}.

> 

> I've been thinking about it for a while, and I know several methods

> using a more traditional programming style (with For, for example), but

> I have no idea if it is possible to make it simple and fast with rule

> substitutions.

> 

> Any idea? 

> 

> Thanks in advance.

> 



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